There is a substantial and on-going need in the electronic arts for dividing an input frequency to produce a lower output frequency. Dividers are much used, for example, in connection with phase-locked loops (PLL's).
The higher the input frequency the more difficult it is to accomplish frequency division. When the input frequency is in the microwave range, as for example above about 0.5 GHz and more typically 1 to 20 GHz or above, the problem of obtaining efficient frequency division is most acute, especially obtaining frequency division across a significant bandwidth of input frequencies.
A further consideration of importance in connection with microwave frequency division is that the components used to provide frequency division should be of a size and character as to be readily integrated in Monolithic Microwave Integrated Circuits (MMIC's). This is especially important for frequencies above about 5 GHz.
It is known to use regenerative analog frequency dividers for microwave applications. Regenerative dividers are described for example in U.S. Pat. Nos. 3,140,447, 3,381,137 and 4,631,500. Regenerative dividers use a feedback loop containing amplification, filtering and mixing functions. However, they suffer from a number of disadvantages well known in the art, as for example, narrow bandwidth and spurious oscillations.
Logic gates can be used for digital frequency division but are generally limited to lower frequencies than analog frequency dividers and thus are not useful over a sufficient range of microwave frequencies.
Parametric analog frequency dividers are also known. For example, a parametric frequency divider employing FET's and operating up to 12 GHz is described in "GaAs Monolithic Analogue Frequency Halver", by Stapelton et al., Electronics Letters, Vol. 22, No. 15, pages 773-774, Jul. 17, 1986. Stapelton's circuit is reproduced as FIG. 1. While this circuit functions, it has some disadvantages.
Thus, a need continues to exist for an improved frequency divider, especially a frequency divider able to operate at microwave frequencies. It is further important that such frequency divider be suitable for implementation as a Monolithic Microwave Integrated Circuit (MMIC). As used herein the term Monolithic Microwave Integrated Circuit and the abbreviation MMIC are intended to refer to a circuit formed of components which can be constructed substantially entirely on and/or in the surface of a substrate utilizing integrated circuit fabrication techniques. Examples of components useful for MMIC's are monolithic transistors, diodes and junction capacitors, and thin (or thick) film capacitors, inductors, resistors and interconnections.